Granular ceramic heat carrier and method for manufacture thereof

ABSTRACT

A granular ceramic heat carrier for use in conjunction with chemical processes, the granules of which heat carrier contain the oxides of aluminum, silicon, chromium and iron, and a method of manufacturing said granular ceramic heat carrier comprising preparing a mix from alumina, fire clay and chrome are powders and a binder.

tates atent .Huzvuk et al.

[ June 13, 1972 [54] GRANULAR CERAMIC HEAT CARRIER AND METHOD FORMANUFACTURE THEREOF [22] Filed: Dec. 20, 1968 [21] Appl.No.: 785,764

[52] US. Cl ..252/71, 106/59, 106/65, 106/66, 106/67, 106/68, 252/455 R[51] Int. Cl. ..C04b 35/10, C09k 3/02 [58] Field of Search ..252/71, 455R; 106/65-68, 59

[56] References Cited UNITED STATES PATENTS 2,272,038 2/1942 Morgan..106/66 2,672,671 3/1954 Robinson... 252/71 2,685,528 8/1954 Robinson106/65 3,184,321 5/1965 Heuer et al. 106/66 X 3,403,213 9/1968 Taylor etal... 106/59 X 3,442,668 5/1969 Fenerty et a1. 106165 X 3,473,938lO/l969 Oberlin 106/65 X OTHER PUBLICATIONS Condensed ChemicalDictionary" pg, 419 7th ed. 1966) Primary ExaminerRichard D. LoveringAttorney-Waters, Roditi, Schwartz & Nissen [57] ABSTRACT A granularceramic heat carrier for use in conjunction with chemical processes, thegranules of which heat carrier contain the oxides of aluminum, silicon,chromium and iron, and a method of manufacturing said granular ceramicheat carrier comprising preparing a mix from alumina, fire clay andchrome are powders and a binder.

10 Claims, N0 Drawings GRANULAR CERAMIC HEAT CARRIER AND METHOD FORMANUFACTURE THEREOF This invention relates to granular ceramic heatcarriers to be used in chemical processes and to methods ofmanufacturing the same.

The aforesaid heat carrier may find application for the pyrolysis ofhydrocarbons with a view to producing ethylene, propylene and acetylene,for the production of inert gases to be used for heat treatment of metalelements and structures, for the manufacture of fuel gases by thecontact pyrolysis of petroleum products and tars, and also in thesynthetic rubber industry as a promoting additive in catalyst systems,etc.

Known in the art is a granular ceramic heat carrier intended for use inchemical processes and characterized in that the granules of the heatcarrier contain alumina and silica; also known is a method ofmanufacturing this granular heat carrier from powdered alumina and fireclay in the presence of a binder.

The known granular ceramic heat carrier is devoid of adequate mechanicalstrength and wear resistance, which disadvantages make the consumptionrate of this material excessively high.

The known granular ceramic heat carrier sufiers from a furtherlimitation of exhibiting low heat resistance.

It is an object of the present invention to obviate the aforementionedlimitations.

It is a further and more specific object of the invention to provide agranular ceramic heat carrier having granules of any desired size andexhibiting high mechanical strength, wear resistance and thermalstability.

This object is accomplished by the provision of a granular ceramic heatcarrier whose granules, apart from silica and alumina, contain,according to the invention, also chromium and iron oxides.

It is expedient to employ a granular ceramic heat carrier containing75-80 percent of alumina, 5-7 percent of silica, 5-10 percent ofchromium oxides and 2-3 percent of iron oxides by the weight of the heatcarrier.

The present granular ceramic heat carrier can be conveniently preparedby a method which comprises blending powdered alumina, fire clay andchrome ore with a binder, the preferred amounts of the pulverantcomponents being as follows:

65-75 percent of alumina, -15 percent of fire clay, and -20 percent ofchrome ore based on the overall weight of the blend.

To prepare a granular heat carrier noted for its enhanced heatconductivity, mechanical strength and wear resistance, it is goodpractice to employ a solution of sodium silicate or potassium silicate,or a mixture thereof.

Where it is desired to obtain a granular heat carrier having granules ofany pre-set size and exhibiting superior mechanical strength and wearresistance characteristics, recourse should be had to a solution ofaluminum sulfate and sulfitecellulose liquor as the binder. In thelatter case, the procedure comprises preparing a mixture of pulverantalumina, fire clay and chrome ore, taking about one-third of theresultant mixture and moistening it with an aluminum sulfate solutionand subjecting it to granulation while feeding simultaneously to thegranulation step the remaining two-thirds of the dry mixture andmoistening the thus obtained granules with sulfitecellulose liquor.

The present method for the manufacture of granular ceramic heat carrieris accomplished in the following manner.

lnto a ball mill are charged and mixed for a period of about 2 hourspowdered components taken in the following amounts, percent by weight:alumina (grain size, below 0.1 mm); 65-75; fire clay (grain size, below0.5 mm), 10-15; and chrome ore (grain size, below 0.1 mm), 15-20.

The resultant dry mix is transferred into a mixer, in which it isstirred for 15 minutes while being moistened, for example, with asolution of aluminum sulfate (sp.gr. 1.22 g/cm), or a mixture ofsulfite-cellulose liquor (sp. gr. 1.22-1.24 glcm and an aluminum sulfatesolution (sp. gr. 1.20-1.22), or a solution of sodium silicate (sp. gr.1.30-1.35 g/cm), or a solution of potassium silicate (sp. gr. 1.30-1.35g/cm), or a mixture of sodium and potassium silicate solutions (sp. gr.1.30-1.35 g/cm The next step consists in discharging the moistened mix(moisture content, about 8-10 percent) from the mixer and trituratingthrough a sieve having 1 mm openings until there is obtained ahomogeneous mass which is thereafter directed to a collector. From thecollector, the mix is fed every 2-3 minutes in 2-3 kg portions to agranulator, in which granulating the mix is effected while moistening(spraying) the resultant granules with one of the aforementionedsolutions having a specific gravity of l.12-1.19 g/cm The sphericalgranules thus obtained are discharged from the granulator, gradedthrough appropriate screens and thereafter subjected to secondarygranulation for a period of 5-10 minutes until they acquire regularspherical shape.

The secondary granulation step having been terminated, the granules aredried at a temperature of 100-120" C and thereafier fired by graduallyraising the temperature to ca. 1,500-1,650 C over a period of 24-36hours, followed by maintaining said temperature for an additional periodof 6-10 hours.

After firing and cooling, the resultant spherical granules from 3 to 30mm in dia. comprise the finished heat carrier.

in order to increase the yield of granulated ceramic heat carrier havingthe pre-set diameter of granules and exhibiting improved performancecharacteristics, the present method may be accomplished in accordancewith the following flow sheet.

In a ball mill there are mixed for a period of about 2 hours powderedalumina, fire clay and chrome ore taken in the proportions and havinggrain sizes specified hereinabove. Approximately two-thirds of the mixthus obtained is transferred into a collector, whereas the remaining mix(about one-third of the total amount) is discharged into a mixer, whereit is moistened, while being stirred for a period of 15 minutes, with asolution of aluminum sulfate (sp.gr. 1.20-1.22 g/cm), or a solution ofsodium silicate (sp.gr. 1.30-1.35), or a mixture of sodium and potassiumsilicate solutions (sp. gr. 1.30-1.35 g/cm").

The resultant moistened mix having a moisture content of ca. 10-16percent is subjected to trituration through a sieve and fed in 2-3 kgbatches every 10 minutes to a granulator. The granulation step iscarried out while feeding from the collectdr the dry mix in 0.5-l kgbatches every 2-3 minutes and moistening (spraying) the resultantgranules with sulfite-cellulose liquor (sp.gr. 1.12-1. l9 g/cm), or asolution of sodium silicate (sp.gr. 1.12-1 19 g/cm), or a solution ofpotassium silicate (sp.gr., 1.12-1.19 g/cm), or a mixture of sodium andpotassium silicate solutions (sp.gr. 1.12-1. 19 g/cm).

Secondary granulation, drying, firing and cooling of the granules arecarried out as disclosed hereinabove. The finished ceramic heat carriergranules are spherical in shape and may have a diameter of from 0.5 to20 mm.

For a better understanding of the present invention, the followingexamples of manufacturing the spherical ceramic heat carrier granulesare given by way of illustration.

EXAMPLE 1 In a ball mill containing 240 kg of steel balls 25 mm in dia.there are mixed for a period of 2 hours 84 kg of alumina powder, 12 kgof fire clay powder, and24 kg of chrome ore 7 powder.

kg of the thus prepared mix is transferred to a collector, while theremaining mix is placed in a mixer and stirred for 15 minutes whilemoistening the mix with 6 lit of an aluminum sulfate solution (sp.gr.1.20 g/cm). The moistened mix is discharged from the mixer andtriturated through a sieve having 1 mm opening until there is obtained ahomogeneous mass which is transferred to a separate collector. From thecollector the moistened mix is fed in batches of 3 kg every 10-12minutes into a granulator having a bowl 1 m in diameter, provision beingmade for feeding simultaneously into the granulator 1 kg batches of thedry mix every 2 minutes and for moistening the thus obtained granuleswith sulfite-cellulose liquor (sp.gr. 1.15 g/cm).

The resultant spherical granules from 4 to 9 mm in dia. are graded onscreens having 4.5 and 8 mm openings. The granules having a diametersmaller than 4.5 mm and greater than 8 mm are triturated on a sievehaving 1 mm openings and the mass thus obtained is recycled back to thegranulation step.

The granules having a diameter in the 5 to 8 mm range are subjected tosecondary granulation with a view to imparting regular spherical shapethereto, followed by drying the granules at a' temperature of 1 20" Cand firing the dried granules by gradually raising the temperature to1,65 C over a period of 36 hours and maintaining the granules at thistemperature for 8 hours, and thereafter cooling the fired granules.

The thus obtained spherical ceramic heat carrier has the followinganalysis, percent by weight:

mp, 79; 2 3 3 c o 9 CaO and MgO 2.5 sio 6.5

Presented below are the essential characteristics of the sphericalceramic heat carrier:

from 4.5 to 7.5 mm from 500 to 700 kg/cm diameter of spheres compressionstrength hereinabove can be used in chemical processes at a temperatureof up to 1,400 C.

EXAMPLE 2.

In the ball mill of Example 1 there are charged and mixed for a periodof 2 hours 84 kg of alumina powder, 12 kg of fire clay powder and 24 kgof chrome ore powder.

80 kg of the thus prepared mix is transferred to a collector, while therest of the mix is charged in a mixer and stirred for 15 minutes whilemoistening the contents of the mixer with 4 lit of a sodium silicatesolution (sp.gr. 1.30 g/cm"). The moistened mix is discharged from themixer and subjected to trituration through a sieve having 1 mm openingsuntil there is obtained a homogeneous mass which is delivered to aseparate collector. From the collector, the moistened mix is fed in 3 kgbatches every 10-12 minutes to a granulator having a bowl I m in dia.,the dry mix from the other collector being simultaneously fed into thegranulator in 1 kg batches every 2 minutes and provision being made formoistening the thus prepared granules with a sodium silicate solution(sp.gr. 1.12 g/cm).

The resultant spherical granules from 4 to 9 mm in dia. are graded onscreens having 4.5 and 8 mm openings. The granules less than 4.5 mm andgreater than 8 mm in dia. are triturated through a sieve having 1 mmopenings and the mass thus obtained is recycled back to the granulationstep.

The granules from to 8 mm in dia. are subjected to secondary granulationwith a view to imparting regular spherical shape thereto, followed bydrying the granules at a temperature of 120 C and firing the driedgranules by gradually raising the temperature to 1,500 C over a periodof 24 hours and maintaining the granules at this temperature for 8hours, and thereafter cooling the fired granules.

The thus obtained ceramic heat carrier in the form of spheres has thefollowing analysis, percent by weight:

Presented below are the essential characteristics of the sphericalceramic heat carrier:

from 4.5 to 7.5 mm from 800 to L000 ltglcrn diameter of spherescompression strength porosity 28-32% refractoriness ca. 1,800 C weightloss of spherical heat carrier after a dwell time of 15 minutes in anair-lift pump 0.2-1

The spherical heat carrier prepared as described hereinabove lendsitself to employment in conjunction with chemical processes involvingtemperatures of up to 1,200 C.

Although the present invention has been described with reference to thepreferred embodiment thereof, it will be readily appreciated by thoseskilled in the art that various changes and modifications may beresorted to without deviating from the spirit and scope of the inventionas disclosed in appended claims.

We claim:

1. A granular ceramic heat carrier which consists essentially of 75-80percent alumina, 5-7 percent silica, 5-10 percent chromium oxides and2-3 percent iron oxides based on the overall weight of said heat carrierand which has a grain size of 4.5 to 7.5 mm, a porosity of 28 to 32percent and a compression strength of 500 to 1,000 kg/cm.

2. A method for the manufacture of a granular ceramic heat carn'er whichcomprises the steps of (1) preparing a dry mix from 65-75 percentpowdered alumina, 10-15 percent fire clay, and 15-20 percent chrome orebased on the overall weight of the dry mix, (2) moistening the dry mixwith a first portion of a binder selected from the group consisting ofaqueous aluminum sulfate, cellulose sulfite liquor and an alkali metalsilicate selected from sodium silicate, potassium silicate and mixturesof the two, said first portion of said binder having a specific gravityof 1.20-1.35 (3) granulating said moistened mix while moistening with asecond portion of said binder having a specific gravity of 1.12-1.19 and(4) subjecting the resultant granules to firing by heating to atemperature of 1,500-1,650 C. over a period of 24-36 hours and holdingat that temperature for 6-10 hours.

3. A method according to claim 2, wherein the binder is a sodiumsilicate solution.

4. A method according to claim 2, wherein the binder is a potassiumsilicate solution.

5. A method according to claim 2, wherein the binder is a mixture ofsodium and potassium silicate solutions.

6. A method according to claim 2, wherein about one-third of the dry mixis moistened with an aluminum sulfate solution and subjected togranulation while feeding simultaneously to the granulator the remainingtwo-thirds of the dry mix and the moistening the resultant granules withsulfite-cellulose liquor.

7. A method as in claim 6 wherein the aluminum sulfate solution has aspecific gravity of 1.20 to 1.22g/cm and the sulfite-cellulose liquorhas a specific gravity of 1.12 to 1.19g/cm".

8. A method as in claim 7 wherein the firing is carried out at 1,650 C.for 8 hours.

9. A method as in claim 2 wherein step (2) comprises moisteningone-third of the dry mix with a first alkali metal silicate solutionbinder having a specific gravity of 1.30 to 1.35 g/cm to obtain amoisture content of 8 to 10 wt. percent, granulating the resultant mix,spraying the granules with a second alkali metal silicate solutionbinder having a specific gravity of 1.12 to 1.19 g/cm whilesimultaneously adding the remaining two-thirds of the dry mix.

10. A method as in claim 9 wherein the firing is carried out at 1,500C.for 8 hours.

t t i k

2. A method for the manufacture of a granular ceramic heat carrier whichcomprises the steps of (1) preparing a dry mix from 65-75 percentpowdered alumina, 10-15 percent fire clay, and 15-20 percent chrome orebased on the overall weight of the dry mix, (2) moistening the dry mixwith a first portion of a binder selected from the group consisting ofaqueous aluminum sulfate, cellulose sulfite liquor and an alkali metalsilicate selected from sodium silicate, potassium silicate and mixturesof the two, said first portion of said binder having a specific gravityof 1.20-1.35 (3) granulating said moistened mix while moistening with asecond portion of said binder having a specific gravity of 1.12-1.19 and(4) subjecting the resultant granules to firing by heating to atemperature of 1,500*1,650* C. over a period of 24-36 hours and holdingat that temperature for 6-10 hours.
 3. A method according to claim 2,wherein the binder is a sodium silicate solution.
 4. A method accordingto claim 2, wherein the binder is a potassium silicate solution.
 5. Amethod according to claim 2, wherein the binder is a mixture of sodiumand potassium silicate solutions.
 6. A method according to claim 2,wherein about one-third of the dry mix is moistened with an aluminumsulfate solution and subjected to granulation while feedingsimultaneously to the granulator the remaining two-thirds of the dry mixand the moistening the resultant granules with sulfite-cellulose liquor.7. A method as in claim 6 wherein the aluminum sulfate solution has aspecific gravity of 1.20 to 1.22g/cm3 and the sulfite-cellulose liquorhas a specific gravity of 1.12 to 1.19g/cm3.
 8. A method as in claim 7wherein the firing is carried out at 1,650* C. for 8 hours.
 9. A methodas in claim 2 wherein step (2) comprises moistening one-third of the drymix with a first alkali metal silicate solution binder having a specificgravity of 1.30 to 1.35 g/cm3 to obtain a moisture content of 8 to 10wt. percent, granulating the resultant mix, spraying the granules with asecond alkali metal silicate solution binder having a specific gravityof 1.12 to 1.19 g/cm3 while simultaneously adding the remainingtwo-thirds of the dry mix.
 10. A method as in claim 9 wherein the firingis carried out at 1,500*C. for 8 hours.